OK, i've had a very quick look at some of your models. Your biggest issue is NGons, especially the wall pieces with cutouts for doors and windows etc.
This is how they look:
This is how i would make them, the red lines are added edges, in Blender you can add them by simply selecting two vertices and pressing J:
You have also exported your cameras with your models, this is a very bad thing to do, it can cause issues and confusion in engines, when exporting you need to make sure you only select the objects you want to export and that you have ticked the selected objects only tick box in the exporting window.
Also, for flat objects with sharp edges like this don't use smooth shaded, keep it on smooth sharp, you don't need smooth shading on hard surface objects like this.
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